Bar codes have been used in a wide variety of applications as a source for information. Typically bar codes are used at a point-of-sale terminal in merchandising for pricing and inventory control. Bar codes are also used in controlling personnel access systems, mailing systems, and in manufacturing for work-in process and inventory control systems, etc. The bar codes themselves represent alphanumeric characters by series of adjacent stripes of various widths, i.e. the universal product code.
A bar code is a set of binary numbers. It typically consists of black bars and white spaces. A wide black bar space may signify a one and a thin black bar or space may signify a zero. The binary numbers stand for decimal numbers or letters. There are several different kinds of bar codes. In each one, a number, letter or other character is formed by a pre-established number of bars and spaces.
Bar code reading systems or scanners have been developed to read bar codes. The bar code may be read by having a light beam translated across the bar code and a portion of the light illuminating the bar code is reflected and collected by a scanner. The intensity of the reflected light is proportional to the reflectance of the area illuminated by the light beam. This light is converted into an electric current signal and then the signal is decoded. Bar codes are read by taking the ratio of the bars width to the width of the adjacent spaces.
Bar codes may be placed on objects with many different types of technology i.e., ink jet printing, laser or LED-based xerography, etc. When bars are recorded on objects with ink jet printers or by LED-based xerographic techniques, the bars will be reproduced differently. The bars have a tendency to grow in width. Consequently, the spaces between adjacent code forming bars become smaller and the code becomes more difficult to read. The prior art has attempted to solve the foregoing problem by incorporating a time compensating set of bars in the body of the bar code. The time compensating bars were used to compute the printer induced growth of the bars and then to compensate for bar growth.
The prior art also utilized pixel shaving techniques to compensate for increases in the size of bar code bars. Pixel shaving techniques were only able to partially compensate for correct increases in the size of bar code bars. The reason for the above is that only complete pixels were removed or added to adjacent code forming bars. Thus, the space between adjacent code forming bars would still not be constant.
Historically postage meters have been mechanical and electromechanical devices that: maintain through mechanical or "electronic registers" (postal security devices) an account of all postage printed and the remaining balance of prepaid postage; and print postage postmarks (indicia) that are accepted by the postal service as evidence of the prepayment of postage.
Soon small business mailers may be able to use their desktop computer and printer to apply postage directly onto envelopes or labels while applying a address. The United States Postal Service Engineering Center recently published a notice of proposed specification that may accomplish the foregoing. The title of the specification is Information Based Indicia Program Postal Security Device Specification, dated Jun. 13, 1996. The Information Based Indicia Program specification includes both proposed specifications for the new indicium and proposed specifications for a postal security device (PSD). The proposed Information - Based Indicia (IBI) consists of a two dimensional bar code containing hundreds of bytes of information about the mail piece and certain human-readable information. The indicium includes a digital signature to preclude the forgery of indicia by unauthorized parties. The postal security device is a unique security device that provides a cryptographic digital signature to the indicum and performs the function of postage meter registers.
Recent studies have shown that the code format tolerances promulgated in the IBIP specification can only be met by some of the available printers. Both resolution (dots/inch) and positional accuracy seem to be the major limiting factors. Furthermore, the printing technology used is yet another major factor, specifically when combined with the type of paper used to form the envelope. Current estimates suggest that 2-3% of the IBIP indicium that are affixed to mail pieces will not be able to be read due to the use of incorrect printers, defective printers or improper envelopes.
Two dimensional bar codes and many other types of codes do not have an element that allows for the increase in width of bar code bars caused by reproducing the bars on objects.